1. Field of Invention
The invention relates to a wiper apparatus for mounting upon motor vehicles, such as passenger cars, buses and trucks.
2. Description of Related Art
In general, a motor vehicle is provided with a wiper apparatus to wipe a window surface such as a windshield. The conventional wiper apparatus comprises a pivot shaft fitted to a sleeve and mounted on a vehicle body side, which shaft is rotatable around its axis. The proximal portion of the pivot shaft is coupled to a link mechanism of a wiper motor serving as a drive source for a wiper arm. The wiper arm is fixedly secured to the tip portion of the pivot shaft and swings for wiping the window surface. Another type of wiper apparatus protrudes the wiper arm and tip portion of the pivot shaft outwardly from the vehicle body side. This latter type poses the problem of directly receiving impacts from external sources resulting in the wiper apparatus breaking down, deforming or otherwise suffering serious damage.
Accordingly, as disclosed in JP-A-11-124013, there has been proposed a motor vehicle wiper apparatus structure in which a brittle portion is included in a depression preventing member, such as a washer, for preventing the pivot shaft from depressing or sinking toward the interior of the motor vehicle with respect to the sleeve. With this arrangement the brittle portion is broken down or sheared, as shown in FIGS. 8 and 9 of the aforesaid publication, or the depression preventing member is deformed to cause the pivot shaft to depress toward the vehicle""s interior side, as shown in FIG. 6 of the aforesaid publication, when a load from outside the motor vehicle exceeds a predetermined value and works on the tip portion of the pivot shaft. The effect is a reduction of impact load upon the wiper apparatus.
However, in JP-A-11-124013, in the case of the breakdown of the brittle portion of the depression preventing member, naturally a large stress (shearing force) operates at the moment of the breakdown, which decreases the effect of reducing damage such as breakdown.
In the case of a construction which makes use of the deformation of the depression preventing member, a large stress does not operate instantaneously unlike the case of the breakdown. This type of arrangement as shown in FIG. 4, includes a stopping groove 14 which is formed in a pivot shaft 13 supported rotatably by a sleeve 12, and a tip portion 16a of a slip-out preventing member (bracket piece) 16 which is fixed by a bolt through a rubber vibration insulator 15 to the body side is inserted into the stopping groove 14. Thus, when a load acts on the pivot shaft 13 from the outside in an axial direction, the direction of the load is in the axial direction of the pivot shaft 13, but is not in a radial direction thereof in which the depression preventing member tip portion 16a can move out of the stopping groove 14. Accordingly, the depression preventing member tip portion 16a is bent locally by an edge portion 14a of the stopping groove 14 with the stopping groove edge portion 14a biting into the edge portion 16a. Then the depression preventing member tip portion 16a is drawn over the stopping groove edge portion 14a and disengages from the stopping groove 14. Thus, not only does a considerable load result, but also difficulty is experienced in controlling this load constantly so that differences among product occur, thereby decreasing the effectiveness of reducing damage such as breakdown. This invention aims to solve these problems.
The invention has been developed in consideration of the above-stated situations and to reduce the likelihood of the problems cited. In accordance with this invention, there is provided a wiper apparatus for a motor vehicle, comprising a sleeve fixedly secured to a vehicle body and a pivot shaft which is supported rotatably in the sleeve wherein the base portion of the pivot shaft is connected to a drive source. The tip portion of the pivot shaft is on the vehicle""s exterior side and holds a wiper arm. For the pivot shaft to be depressed toward the vehicle""s interior side with respect to the sleeve, a load exceeding a predetermined value works axially on the pivot shaft from the vehicle""s exterior side. A depression preventing member is interposed between the pivot shaft and the sleeve and is deformed when receiving the load that depresses the pivot shaft. A deformation space is secured between the pivot shaft and the sleeve for enabling the deformation of the depression preventing member to occur smoothly.
With this structure, the depression of the pivot shaft is achieved by the smooth deformation of the depression preventing member, which relieves damages such as a breakdown.
The deformation space can be secured between the pivot shaft and the sleeve with room enough to include a bearing bush whereupon, for securing the deformation space, it is possible to use the bearing bush space directly so that an increase in deformation space size is avoidable.
In addition, an inner circumferential portion of the depression preventing member is fitted in a stopping groove made in the pivot shaft, while an outer circumferential portion thereof is brought into contact with a tip portion of the sleeve. The stopping groove is made wide in an axial direction to constitute a portion of the deformation space. In consequence, deformation of the depression preventing member occurs as the depression preventing member is brought into contact with two points, namely, the tip portion of the sleeve and the vehicle""s exterior side end portion of the stopping groove. This results in deformation of the depression preventing member occurring smoothly while a local bending is avoided, thereby reducing damage to the wiper apparatus.